Asphalt is a residue which is obtained after most of volatile oils in components of crude oil are evaporated, wherein the asphalt has physical properties in which it maintains a liquid or semi-solid state having high viscosity at high temperature but it hardens at room temperature or less. Also, since asphalt has characteristics in which plasticity is good, water resistance, electrical insulation, and adhesiveness are high, and chemical stability is excellent, asphalt has been widely used in construction materials such as a paving material or a waterproof material. However, asphalt has limitations in that plastic deformation occurs during use when the asphalt is exposed to high temperatures for a prolonged period of time and cracking occurs at low temperatures due to an external impact.
In order to address the above limitations, research to improve the physical properties of asphalt by adding various polymers has currently been conducted.
For example, there is a method of using a vinyl aromatic hydrocarbon-conjugated diene block copolymer, such as a styrene-butadiene-styrene (SBS) block copolymer, as a modifier or impact modifier for improving physical properties of an asphalt composition.
In general, in order to use the SBS block copolymer in the asphalt composition, compatibility with asphalt is basically and essentially required. In a case in which the SBS block copolymer has excellent compatibility with asphalt, processing time may be reduced and the effect of improving the physical properties of asphalt may be high.
However, while advancement of oil refining facilities has been continuously made due to an increase in oil prices and energy saving policy, the amount of asphaltene in asphalt, as a refining byproduct, has been increased. Since the asphaltene, as an aggregate of aromatic hydrocarbons, includes a large amount of polar functional groups at the ends thereof, the asphaltene has very low compatibility with the SBS block copolymer having no functional group. Thus, processing time of the asphalt composition may not only be significantly increased, but degradation of the quality of the asphalt, for example, a decrease in elasticity of the modified asphalt composition, may also occur.
With respect to the above limitations, a method of controlling molecular weight of the SBS block copolymer or changing a molecular microstructure of the block copolymer so as to provide a coupling effect, or a method of adding an additive, such as oil, as a processing aid, has been proposed. However, since a modification method for each asphalt with quality deviations must be developed even if the above methods are used, the above methods may not be the ultimate solution.
Thus, there is an urgent need to develop an SBS block copolymer as an asphalt modifier having excellent compatibility with asphalt.